A communication system having multiple nodes connected to a communication line is known. For example, in a communication system disclosed in JP-A-H4-292236, a master station is connected to multiple nodes (remote stations) via communication lines. In this communication system, each node is provided with a sleep function to reduce dark current. Specifically, when the sleep function detects that the master station stops communication for a predetermined continuous time period, the node is automatically put into a sleep mode.